U0408
Invalid Data Received From Throttle Actuator Control Module
- Severity
- Critical
- Driving
- Drive only to a garage
The throttle actuator control module is sending data that the module storing this code can tell is wrong. The message is arriving, so the network and the wiring between them are working - but something in it fails a plausibility check: a value outside the range it could physically take, a failed checksum, or a message counter that stopped advancing. That is what separates this from a lost communication code, where the message stops arriving altogether. This code is stored by the module *receiving* the data and it names the module that *sent* it, so it points away from itself. The fault is usually in the throttle actuator control module, or in a sensor feeding it, rather than in the module that noticed. Electronic throttle control has no mechanical cable behind it, so the module will not open the throttle on a value it cannot verify. It falls back to a restricted mode - typically a fixed low idle and very limited response - which is deliberately conservative and deliberately obvious.
Possible causes
- CommonA fault inside the throttle actuator control module, or in a sensor feeding it, so it passes on a reading that is wrong
- CommonThe throttle actuator control module has its own stored fault codes that explain why its data is bad
- CommonLow or unstable system voltage - a module starved of a steady supply produces nonsense values
- CommonCorroded or water-damaged connector at the throttle actuator control module, corrupting the message content
- PossibleSoftware or calibration mismatch after the throttle actuator control module was replaced, updated or coded
- PossibleDamaged wiring, or a repair that disturbed the bus pair
- PossibleInterference from a badly-fitted aftermarket accessory spliced into the bus
- RareA fault in the receiving module, which is misjudging data that is actually good
What you might notice
- Severely reduced power - the car barely responding to the accelerator
- Elevated or erratic idle
- Red or amber throttle warning light
- The car entering limp mode as soon as it is started
- Warning light on for the system that depends on the data
- The affected function switching itself off
- Fault codes stored in more than one module
What to check, in order
- Read the codes from every module on the vehicle, not just the engine. This code names the throttle actuator control module as the source, and the throttle actuator control module almost always has its own code saying why its data is wrong. That code, not this one, is the one to fix.
- Check battery voltage and the earth points before suspecting any module. A supply that sags makes modules produce implausible values, and it sets invalid-data codes across several unrelated systems at once.
- If more than one module is reporting invalid data, look at the power supply and the bus rather than at the modules. Modules do not fail in groups; shared feeds, earths and bus wiring do.
- Find out whether anything was recently fitted, replaced, updated or coded. A replacement module carrying the wrong calibration sends data in a range or format the rest of the vehicle does not expect, and this code is often the first sign of it.
- Inspect the connector at the throttle actuator control module for corrosion and water ingress. A partly-corroded pin corrupts the content of a message while the message itself still arrives on time - which is precisely this code rather than a lost communication code.
- Do not replace the throttle actuator control module on the strength of this code alone. It is the accused, not the convicted. Confirm the data it is sending is actually wrong - by reading its own codes and its live data - before spending money on it.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.